Total (as opposed to per-student) student loan debt by sector (public, private non-profit, private for-profit) is obviously going to be much higher for the public schools, since the public schools enroll far more students. See figure 4 of http://nces.ed.gov/programs/coe/indicator_cha.asp . In 2014, there were 13.2 million undergraduates at public schools, 2.8 million in private non-profit schools, and 1.3 million in private for-profit schools.